This invention relates to a single-stage process for the production of polyamines containing aromatically bound primary amino groups by the hydrolysis of compounds containing terminal aromatic isocyanate groups (NCO-content 0.5 to 40 wt. %) in a single-stage in the presence of tertiary amines and, optionally, water-soluble ethers and, optionally, co-catalysts. The invention also relates to polyamines produced by this process.
It is known that aromatic isocyanates can be converted into primary aromatic amines by acid hydrolysis. However, this reaction does not proceed to completion because the amine formed during hydrolysis further reacts with the unreacted isocyanate to form the corresponding urea. This further reaction cannot be suppressed even by using excess, strong mineral acid. An example of such an acid hydrolysis can be found in Japanese Patent No. 55 007-827.
German Offenlegungsschrift No. 1,270,046 describes a process for the production of primary aromatic amines containing polyalkylene glycol ether segments In this disclosed process, reaction products of aromatic diisocyanates or triisocyanates with polyalkylene glycol ethers and/or polyalkylene glycol thioethers (preferably those having molecular weights of from 400 to 4000) are reacted with secondary or tertiary carbinols. The product of this reaction is subJect to thermal cleavage at elevated temperatures in an inert solvent (and optionally acid catalysts). In addition to the high cleavage temperature, the disadvantage of this process lies in the fact that the thermal cleavage of the urethanes is accompanied by formation of flammable, readily volatile alkenes which are explosive in admixture with air.
German Offenlegungsschrift No. 1,694,152 describes the production of prepolymers containing at least two terminal amino groups by reacting hydrazine, aminophenyl ethylamine or other diamines with an NCO-prepolymer of a polyether polyol and polyisocyanate (NCO:NH-ratio=1:1.5 to 1:5). In this disclosed process, unreacted amine must be carefully removed in another step because the unreacted amine both reacts with and catalyzes the reaction with polyisocyanates to a considerable extent (thereby leading to short processing times).
Another possible synthesis for polyamines containing urethane groups is described in French Patent No. 1,415,317. In this disclosed process, NCO-prepolymers containing urethane groups are converted with formic acid into the N-formyl derivatives which are then hydrolyzed to form terminal aromatic amines. The reaction of NCO-prepolymers with sulfamic acid according to German Offenlegungsschrift No. 1,155,907 also leads to compounds containing terminal amino groups. Relatively high molecular weight prepolymers containing aliphatic secondary and primary amino groups may be obtained according to German Offenlegungsschrift No. 1,215,373 by reacting relatively high molecular weight hydroxyl compounds with ammonia under pressure at elevated temperatures in the presence of catalysts. According to U.S. Pat. No. 3,044,989, reacting relatively high molecular weight polyhydroxyl compounds with acrylonitrile, followed by catalytic hydrogenation yields prepolymers having secondary and primary amino groups. Relatively high molecular weight compounds containing terminal amino groups and urethane groups may also be obtained by reacting NCO-prepolymers with enamines, aldimines or ketimines containing hydroxyl groups, followed by hydrolysis (German Auslegeschrift No. 2,546,536 and U.S. Pat. No. 3,865,791). In another possible synthesis, aromatic polyamines containing urethane and ether groups are produced by opening the ring in the reaction of isatoic acid anhydride and diols. Polyamines of this type are described, for example, in U.S. Pat. No. 4,180,644 and in German Auslegeschriften Nos. 2,019,432; 2,619,840; 2,648,774. and 2,648,825. The poor reactivity of aromatic ester amines obtained in this way is disadvantageous in numerous applications.
The reaction of nitroaryl isocyanates with polyols, followed by reduction of the nitro groups to aromatic amino groups, is also known (U.S. Pat. No. 2,888,439). The major disadvantage of this process is the high cost of the reduction step.
It is also known that certain heteroaromatic isocyanic acid esters can be converted into heteroaromatic amines by basic hydrolysis. However, the hydrolysis conditions described by H. John in J. Prakt. Chemie 130, 314 et seq. and 332 et seq (1931) for two specific, heteroaromatic monoisocyanic acid esters are both totally unsuitable for the conversion of poly-NCO-compounds into aliphatic and/or aromatic amines and dangerous.
Two of our own proposals (German Offenlegungsschrift No. 2,948,419 and P No. 30 39 600) are multistage processes for the production of polyamines. In these processes, NCO-preadducts are hydrolyzed with excess base (alkali hydroxides) to form carbamates, acidified with mineral acids or ion exchanger resins in equivalent quantities or in greater quantities exceeding the quantity of base to decompose the carbamates, optionally neutralized with base and the product polyamine isolated.
The known processes for the production of polyamines described above are all complicated. Even though our own process for converting polyisocyanates into polyamines is simpler than other prior art processes, it would still be desirable to achieve further simplification to enable polyamines to be produced economically and efficiently. It would therefore be particularly advantageous to have a single-stage process (as opposed to the customary multistage processes) for producing polyamines.
Until now, all attempts to obtain satisfactory yields of polyamines by the direct hydrolysis of polyisocyanates in a single-stage have been unsuccessful. Instead of the desired hydrolysis products, the products obtained have been only partially homogeneous, did not flow freely and contained only urea groups with very few, if any, amino groups (see Comparison Examples, infra). The reason for this appears to be that the isocyanate/amine reaction is considerably faster than the isocyanate/water reaction.